Only set the server url if it exists in the config

Author: GrahamCampbell

src/ParseServiceProvider.php

@@ -63,7 +63,10 @@ protected function setupParse()
         $config = $this->app->config->get('parse');
 
         ParseClient::initialize($config['app_id'], $config['rest_key'], $config['master_key']);
-        ParseClient::setServerURL($config['server_url']);
+
+        if (isset($config['server_url'])) {
+            ParseClient::setServerURL($config['server_url']);
+        }
     }
 
     /**